Under pressure drilling or hot tapping is the process of drilling into a pressured pipe or vessel using special equipment and procedures to ensure that the pressure and fluids are safely contained when access is made. The most common example of a hot tap is into a pressured pipeline. A typical hot tap assembly consists of a saddle assembly with a doughnut-type elastomer pack off, two outboard full-bore flanged valves, a tee assembly and the hot tapping device. A conventional hot tap device has a polished rod and pack-off assembly which allows movement in the longitudinal direction, as well as rotation while maintaining a seal. A drill bit is installed on the end of the polished rod to drill into the vessel. The means to turn the polished rod may be manual, or by air or hydraulic-generated torque. A threaded sleeve feeds the polish rod assembly and provides the force to resist the pressure area effect that would tend to blow out the polished rod.
Typical hot tap units are built for surface and onshore work. Subsea conditions present different and additional challenges. Most current hot tap units can not be operated by remotely operated vehicles (ROVs) and require full manual operation by the diver. This requires considerable physical exertion and time by the diver. The current units also require personnel to be at or close to the pressure containing body, exposing them to potentially dangerous conditions. Current designs also require divers to possess a more technical background and more training than their surface or onshore counterparts in order to address possible contingencies. Moreover, conventional multiple piece component saddle clamps that are attached with multiple bolts or fixtures, common to conventional hot tap units, are cumbersome and difficult to attach to a piece of tubular during subsea operations.